Air Conditioning Not Cooling or Heating: What to Check Before You Call
Before you book a visit, there are five things you can safely check yourself. If none of them is the answer, here is what a flashing light means, when to switch off and call, and what happens on a call-out.
The short answer
- Start with the remote: the right mode, a set temperature the room has not already reached, and no timer.
- Then rinse the filters, clear anything from around the outdoor unit, check that the power to the system is on, and switch it off for a minute.
- In winter, an outdoor unit that frosts over and pauses for a few minutes is defrosting, which is normal.
- The remote and the filters are yours to check. Everything behind the panels, the drain, the refrigerant and the electrics are an engineer’s job.
- Hissing, ice on the pipes, a burning smell or a breaker that keeps tripping: switch it off at its isolator and call us. The isolator is the switch on the wall that cuts the power to the system, usually beside the outdoor unit and sometimes indoors. If you cannot find one, use the system’s own breaker in the fuse box.
Five checks you can make yourself
First, if you can smell burning, hear hissing that carries on, or see water coming from the indoor unit, do not make these checks. Switch the system off at its isolator and go straight to When to stop and call.
If the room is for a baby, an older person or someone unwell, and it is very hot or very cold, do not wait on these checks: move them to another room and call us.
Work through them in this order. None of them needs a tool, and none goes further into the unit than its filters.
1. The mode and the temperature on the remote
Look at the remote’s display. It should show cooling (usually a snowflake) or heating (usually a sun). Fan-only (a fan) and dry (a water drop) move air without really cooling or heating it, and auto lets the unit choose, which on a mild day can be the opposite of what you wanted.
Then check the set temperature: below the room’s temperature for cooling, above it for heating. Look for a timer or a sleep setting too, which can switch the unit off or let the temperature drift by itself. If the display is faint or blank, change the remote’s batteries.
If one outdoor unit serves several rooms, every indoor unit has to be in the same mode: one set to cooling will stop another from heating.
In heating, give it a few minutes. The indoor fan waits until the unit is warm, so that it does not blow cold air at you.
2. The filters
Blocked filters starve the unit of air, so it blows weakly and cools or heats poorly.
Most wall units need a step to reach. Use a stepladder on a firm, level floor, never a chair or the bed, and do not hold on to the unit. If the unit is in the ceiling or too high to reach safely, leave the filters for a service visit.
Switch the unit off at the remote, then at its isolator, so that it cannot start while your hands are near it. On a wall-mounted unit, lift the front panel until it stays open and slide the mesh filters out. Do not touch the metal fins behind the filters: they are sharp and they bend.
Rinse the filters under a lukewarm tap and let them dry fully in the air, not on a radiator, in the sun or with a hairdryer, which can warp them. Slide them back until they sit flat, close the panel and switch the power back on.
That is as far into the unit as you should go: take no other cover off.
Not sure which type of unit you have? See the types of air conditioning unit.
3. The outdoor unit
The outdoor unit needs air flowing freely through it. Without touching the unit itself or putting anything through its grille, move away leaves, bins, boxes, garden furniture or snow that are against it. The fan can start without warning. If the unit is on a roof or high on a wall, do not climb to it.
In cold, damp weather the outdoor unit frosts over and the system pauses for a few minutes to melt it. Steam, dripping water and a fan that has stopped are a defrost, and normal. Never chip the frost off or pour hot water over it.
What is not normal is an outdoor unit that stays encased in ice, or one whose fan never turns.
For what a defrost looks and sounds like, see defrost in our winter heating guide.
4. The isolator switch and the fuse box
Most systems have their own isolator: the switch on the wall that cuts the power to the system, usually beside the outdoor unit and sometimes indoors. It is easily switched off by mistake, so check that it is on. If you cannot find one, look for the system’s own breaker in the fuse box.
Then look in your fuse box (consumer unit) for a breaker that has tripped. You can reset it once, unless you have noticed a burning smell or water coming from the indoor unit. If it trips again, straight away or days later, leave it off and call us: a breaker that keeps tripping is protecting you from a fault.
5. A power-off reset
If a light is flashing or the remote shows a code, film it or write it down first, because switching the power off clears it.
Switch the system off at the remote, then at the isolator. Wait a full minute, switch the isolator back on, and start the system from the remote.
Most units then wait a few minutes before the outdoor unit starts, to protect the compressor, so give it five minutes before you judge it.
Error lights and codes
If a light on the indoor unit keeps flashing and the unit will not run, or the remote or the wall controller shows a code, such as a letter and a number, the system has usually found a fault and is telling you what kind. Not every flashing light is a fault. One that flashes for a few minutes in cold weather and then stops is usually the unit defrosting, and where one outdoor unit serves several rooms, a flashing light can mean two rooms are set to opposite modes.
The flash pattern or code is different for every make and model, which is why there is no table of them here: the same code can mean one thing on one make and something else on another. What helps is telling us exactly what you see:
- which light flashes, what colour it is, and how many times before it pauses;
- any code on the remote or the wall controller;
- the make and model, from the rating label on the side of the indoor unit or behind its front cover (film the lights first, then isolate the power before you open it).
A short video of the lights, or a photo of the code and the label, tells us most of it. A power-off reset clears a one-off glitch. If the same code comes back, it is a real fault, and resetting it again will not fix it.
When to stop and call
If you notice any of these, switch the system off at its isolator, leave it off, and call us on 0161 987 7786 or message us on WhatsApp on 07766 395693:
- A hissing that carries on, or ice on the pipes or the indoor unitEither can mean the system is short of refrigerant. If the hissing is indoors, open a window and keep flames and gas hobs out of use in that room until we have been.
- A breaker that trips again after one resetIt is cutting the power because something is wrong.
- A smell of burning, hot plastic or fishElectrical parts give off these smells as they overheat.
- Water dripping from the indoor unitThe drain is blocked, or ice inside the unit is melting.
- A grinding or rattling noise, or an outdoor unit that hums with its fan still when it is not defrostingA defrost stops the fan for a few minutes, about fifteen at most, and only when there is frost to melt. Otherwise a part has probably failed or come loose, and running it can do more damage.
If you see smoke or flames, or a burning smell carries on with the power off, leave the room, close the door and call 999. If you cannot reach the isolator safely, switch the system’s breaker off at the fuse box instead.
Refrigerant and electrics are an engineer’s work. By law, only an F-Gas certified engineer may work on the refrigerant, and the wiring inside both units carries mains voltage. Please do not take any cover off beyond the filter panel, and do not try to clear the drain yourself.
If water is dripping indoors, or the unit smells musty, see dripping water or a musty smell.
What happens on a call-out
Tell us what the system is doing, what you have already checked, any error code, and the make and model. Call us on 0161 987 7786, message us on WhatsApp on 07766 395693, where you can send the photos and the video too, or use the contact form. For an urgent breakdown we can often come the same day.
A fault usually cannot be priced until it has been seen, so a repair starts with a visit to find it. That visit has a call-out and diagnosis fee, and our price page shows the fee for your postcode. It covers the visit and finding the fault. If you go ahead with the repair, we take the fee off its price.
Once we have found the fault, we tell you what the repair involves and what it will cost, and you decide whether to go ahead. Our repairs carry a 12-month warranty.
Video transcript
If your air conditioning isn’t cooling or heating, try these five checks before you call.
But if you smell burning, hear hissing that carries on, or see water coming from the indoor unit, switch off and call instead.
First, the remote. Check the mode: a snowflake for cooling, a sun for heating. Then check the temperature, and that no timer or sleep mode is on.
Second, the filters. Switch off at the isolator, the switch that cuts the power to the system. Stand on a stepladder, never a chair. Lift the front panel and slide them out. Rinse them, and let them dry in the air before they go back.
Third, the outdoor unit. Move leaves, boxes and snow away from it, without touching the unit. In winter it may frost over, pause, and steam. That’s a defrost. It’s normal, and it carries on by itself.
Fourth, the power. Check the isolator, usually by the outdoor unit, is on. Then look in your fuse box. A tripped breaker can be reset once.
Fifth, a reset. Note any flashing light or code first. Then switch off at the isolator, wait a minute, and switch back on.
The remote and the filters are yours to touch. Leave the rest to an engineer. Stop and call us for hissing that carries on, or ice on the pipes. A breaker that trips again, a smell of burning, or water indoors. Or an outdoor unit that hums with its fan still, and no frost on it.
Tell us the error code, or which light is flashing. We can often come the same day.
Arctic Air Conditioning. Cool in summer, warm in winter.
Frequently asked questions
Why is my air conditioning running but not cooling?
Start with the remote: it should be in cooling mode, not fan-only or dry, with the set temperature below the room’s. Then rinse the filters and make sure nothing is blocking the outdoor unit. If it still blows air that is not cold, switch it off and call us, because it needs an engineer.
Why has my air conditioning stopped heating?
In cold, damp weather it pauses for a few minutes to defrost the outdoor unit, then carries on by itself. That is normal. If it stays off, or the air never warms up, check that the remote is in heating mode with the set temperature above the room’s, then make the other checks on this page.
What does a flashing light on my air conditioning mean?
A light that keeps flashing while the unit will not run usually means the system has found a fault. The pattern or code is different for every make and model, so tell us exactly what you see, with the make and model, and we will know where to start. A light that flashes for a few minutes in cold weather and then stops is usually the unit defrosting, and where one outdoor unit serves several rooms, a flashing light can mean two rooms are set to opposite modes.
How do I reset my air conditioning?
If a light is flashing or the remote shows a code, film it or write it down first, because switching the power off clears it. Then switch the system off at the remote and at its isolator, wait a full minute and switch it back on. Most units then wait a few minutes before the outdoor unit starts. If the fault or the same error code comes back, call us and do not keep resetting it.
Can I top up the refrigerant myself?
No. By law, only an F-Gas certified engineer may work on the refrigerant. A system does not use refrigerant up, so if it is short there is a leak, and the leak has to be found and repaired.
How much does an air conditioning call-out cost?
A repair starts with a visit to find the fault, which has a call-out and diagnosis fee. The fee for your postcode is shown on our price page, and if you go ahead with the repair we take it off the repair’s price.
How quickly can you come out?
Often the same day for an urgent breakdown. Message or call us with what the system is doing and any error code, and we will tell you when we can be there.
Still not working?
Send us the make and model, what the system is doing and any error code. We can often come the same day.
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